1. Field of the Invention
The present invention relates generally to fluid flow and control, and more particularly, to a fluid flow control system suitable for use in ultra-pure or corrosive applications.
2. Description of Related Art
Many industries such as semiconductor, pharmaceutical, and bio-technology experience fluid delivery problems due to typically low flow rates, the use of abrasive chemical fluids, the use of corrosive chemical fluids, and the need for contaminant free, accurate, compact, and real-time fluid delivery and/or blending systems.
For example, Chemical-Mechanical Planarization (CMP) is a critical process in the semiconductor industry that involves a process to flatten the wafer surface of a semiconductor. In most applications, a slurry-coated polishing pad rotates at a controlled speed against the semiconductor wafer to flatten the surface. The slurry contains chemicals that soften the surface chemically as well as abrasives that work with the polishing pad to mechanically polish the surface. For CMP to work perfectly, the mechanical and chemical polishing must work together in a delicate balance any changes to this balance can cause damage to the wafer or reduce yield. If there is no slurry, then all of the polishing is mechanical and it would be like polishing glass with sandpaper. If there is too much slurry, most of the polishing is chemical and again the balance is off. The polishing rate of the wafer is highly dependent upon the delivery rate of the fluid and the total amount of fluid delivered during a polishing operation.
For processes such as CMP, the slurry delivery system typically includes a positive displacement pump, such as a peristaltic pump, to draw the slurry from a vessel and apply it to the polishing pad. The pump moves the fluid at a more or less constant rate depending on the speed of the pump, though the peristaltic pumping action causes a pulsation in the fluid delivery rate. Since the peristaltic pump is a volumetric fluid delivery system, the amount of fluid varies with changing conditions such as the pump tube age, the pump tube temperature, the fluid composition, the pump motor speed, the level of fluid in the vessel, pump calibration, etc.
Moreover, in many CMP and similar processes, fluid such as slurry is supplied in a circulating overhead loop. Such slurry loops are often driven with an air actuated diaphragm pump. Several CMP tools may be driven from the same loop. Pressure in the loop my change when one tool draws slurry. This change in loop pressure may affect the slurry flow rate on another tool connected to the same loop.
All of these influences on process flow rate are believed to reduce wafer yield in CMP processes. Therefore, there is a need for fluid delivery system that addresses shortcomings associated with the prior art.